Cultivation of fish ciliate parasites: Progress and prospects

Abstract

Ciliates are considered the most harmful parasites of fish, causing mass mortalities and thus substantial economic losses to the aquaculture and ornamental fish industries. To better elucidate their pathogenic mechanisms and facilitate the development of effective prevention and control strategies, it is essential to apply novel technologies to ensure the continuous and sufficient supply of parasite specimens. This review discusses the latest research progress in the artificial culture of six important parasitic ciliates affecting both freshwater and marine fish globally: Ichthyophthirius multifiliis, Cryptocaryon irritans, Chilodonella (C. hexasticha, C. piscicolaand C. uncinata), Balantidium ctenopharyngodoni, Scuticociliatida gen. spp., and Tetrahymena spp. Methods for in vitro and in vivo culture as well as cryopreservation/preservation (depending on the specific species) of these organisms are described herein. Challenges and future applications of parasite culture are also discussed.

In Vitro Assessment of Berberine against Ichthyophthirius multifiliis in Goldfish

“…The disease caused by I. multifiliis probably brings about more damage to freshwater fish than any other eukaryotic pathogen [ 2 , 3 ]. There are two main strategies for the treatment of the disease: one is aiming at the parasitic trophont stage within the host′s epithelium, while the other is targeting the external stages where the parasite is free-living [ 2 , 4 ]. However, the trophonts in the epithelium are protected both by the mucus secreted by the fish and the proliferation of epithelial tissue, so it is difficult for drugs to kill trophonts through the epithelial tissue.…”

“…(3) Protomont secretes a cyst wall to become a tomont. (4) Tomont undergoes binary fission, producing large numbers of theronts to invade fish again (cited from Li et al [ 4 ]).…”

“…It causes ichthyophthiriasis, commonly known as the “white spot disease”, which can cause great economic losses to the global aquaculture industry [ 1 , 2 , 3 ]. It has four developmental stages ( Figure 1 ): a parasitic trophont, a free-swimming protomont, a reproductive tomont, and an infective theront [ 3 , 4 ]. When the trophont matures, it naturally sheds itself from the host and becomes a free-swimming protomont; when the protomont attaches itself to a flat surface, it soon transforms into a tomont.…”

“…The tomont then undergoes binary fission, producing hundreds of daughter cells called tomites, which further form infectious theronts. Theronts invade the epidermis of susceptible fish, and then rapidly transform into trophonts to complete their entire life cycle [ 2 , 4 , 5 , 6 ].…”

Comparison of droplet digital PCR and real‐time quantitative PCR for quantitative detection of the parasitic ciliate Ichthyophthirius multifiliis in the water environment

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Ichthyophthirius multifiliis (commonly known as "Ich") is one of the most harmful ciliate parasites of freshwater fish. It has a broad host range and infects many fish species with high economic value in tropical, subtropical, and temperate regions (Li et al, 2022;Matthews, 2005). The life cycle of Ich can be divided into three distinct stages: a parasitic growing trophont, a binary fission encysted tomont, and a free-swimming infective theront (Buchmann et al, 2001).

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